This invention relates generally to the field of appliance control circuits and more particularly to a circuit including a microcontroller operable for monitoring the contact posture of an access door actuated switch. The microcontroller will prevent operation of the appliance if monitoring of the access door actuated switch indicates that the contacts have not been actuated between the open and closed postures during a predetermined period of time.
The prior art relating to appliances has generally required that an access door actuated switch be in the closed posture before the appliance can be operated. Grabeck in U.S. Pat. No. 3,627,960, issued Dec. 14, 1971, teaches the closing of an access door to actuate a switch for conditioning the appliance control circuitry. In this system the switch must be closed to indicate a closed access door prior to operation. There is no teaching of a microcontroller for checking the posture of the switch and for ensuring that the switch contacts are operable between open and closed postures which is an indication of the condition or operability of the switch.
Ellingson et al, in U.S. Pat. No. 4,510,777, issued Apr. 16, 1985 and assigned to the assignee of the instant invention, disclose an appliance controlled by a microcontroller. In this appliance, a first switch is closed when the access door is physically operated to a closed position. Closing the access door positions a latch member for locking the access door in the closed position. A solenoid is then actuated by the microcontroller to lock the access door and close the contacts of a latch switch to provide an access door latched signal to the microcontroller. This latch switch is interrogated by the microcontroller prior to actuating the solenoid for confirming the proper operability of the latch switch. The circuit does not, however, teach the direct interrogation of the access door actuated switch by the microcontroller for determining the proper operability thereof.
It is believed that there has been no teaching of a microcontroller-based appliance control circuit wherein the microcontroller is operable for directly monitoring the contact posture of an access door actuated switch and for preventing operation of the appliance in the event that the switch is not functional.